1. Field
This invention pertains generally to radiation detection, and more particularly to direct ion storage (DIS) dosimeters, and most particularly to their fabrication and data retrieval. The invention also pertains to radiation detection systems and methods based on multiple dosimeters, including multiple DIS dosimeters.
2. Description of Related Art
There are many different types of radiation detectors or dosimeters for monitoring exposure to hazardous ionizing radiation, such as x-rays, gamma rays, electrons and neutrons. These range from simple colorimetric film or badge dosimeters to complex electronic devices. Some devices are real-time; others show a cumulative exposure over a long period of time. A wide range of dosages may be detected.
One particular type is the direct ion storage (DIS) dosimeter, as shown in U.S. Pat. No. 5,739,541. A DIS dosimeter is based on a MOSFET with a floating gate on which a charge is placed. The surface of the gate is open to a space containing air or other gas, usually enclosed in a chamber. Ionizing radiation incident on the air or gas produces charge carriers that recombine with and thereby change the charge on the gate. The change in gate charge is detected and provides a measure of the incident radiation dosage. While an effective dosimeter, the DIS dosimeter has not been widely used because of the laborious (typically manual) and expensive fabrication process starting with a MOSFET transistor, altering the transistor to expose the gate, and hermetically sealing the modified transistor in a chamber.
There are many applications for dosimeters, from safety monitoring to industrial process monitoring to medical imaging and radiotherapy. A major application is personal dosimetry for people who may be exposed to radiation; these include medical workers and patients. At present, dosimeters are usually exchanged on a periodic basis with new dosimeters, and the old dosimeters are sent to a service provider who reads the dosimeters and provides data back to the user. Thus there is a lot of handling and transportation of the dosimeters.
One particular application of great interest today is the detection of potential terrorist threats using nuclear materials. Since there are many threat points, including airports, sea ports, border crossings, subways, large public buildings, shopping malls, and sports arenas, and many ways of transporting contraband nuclear material, including vehicles, shipping containers, luggage, and people, an effective system requires many dosimeters and real time data recovery. The military could also use dosimeters to locate nuclear materials and to monitor exposure of troops in the field.
To be widely used, a dosimeter should be low cost and easy to manufacture. Furthermore, to be effective, it must be easy to obtain data from the dosimeters in real time and to communicate this information to a collection point. In some cases the dosimeters may be widely distributed from the collection point; in other cases the dosimeters may all arrive at a common location. It would be particularly useful if the data could be collected using state of the art telecommunications technology, e.g. the Internet.
Therefore, it is desirable to provide a DIS dosimeter design that is low cost and easy to manufacture.
It is also desirable to provide a DIS dosimeter that has easy data readout capability, including a DIS dosimeter with Internet connectability or other telecommunication interfaces.
It is further desirable to provide a system that can read a plurality of dosimeters in different locations or at a common location.